Dams spur more invasions by new species: study

September 3rd, 2008 - 3:43 pm ICT by IANS  

Washington, Sep 3 (IANS) The growing number of dams is increasing the number of invasive species and the speed with which they spread, threatening natural lakes, said a study. The team led by Colorado University looked at data from 4,200 lakes and more than 1,000 impoundments across Wisconsin and the upper peninsula of Michigan. Besides, more than 80,000 large dams and some 2.5 million smaller impoundments sit across the US, the study said.

The study showed non-indigenous species are up to 300 times more likely to occur in impoundments than in natural lakes, increasing the invasion risks for natural lakes.

The results showed increasing occurrence of such species in impounded water, creating “stepping-stone habitats” for them in natural lakes, ponds and waterways in the region, said University’s assistant professor Pieter Johnson, co-author of the study.

The researchers looked at invaders like Eurasian zebra mussel, a urasian water plant known as water milfoil, Eurasian spiny water flea, the rusty crayfish and the rainbow smelt.

Such freshwater invaders often have direct negative effects on lake ecosystems, including reduced fishing success, changes in water clarity and fouling of fishing gear and water-pumping equipment, Johnson said.

Zebra mussels recently jumped to reservoirs in the West, including Colorado, said Johnson, leading to mandatory boat inspections at some landings.

The other invaders are either already in Colorado - the rainbow smelt and water milfoil - or have a high probability of being introduced, like the spiny water flea and rusty crayfish, he said.

“We believe impoundments may be functioning as ‘hubs’ for freshwater invaders, aiding their spread and establishment into natural water bodies,” said Johnson.

The researchers wrote that “reservoir construction and the conversion of free-flowing rivers to standing waters may ultimately facilitate the spread of invasive species across the landscape.”

Dam construction and biological invasions are major contributors to the biodiversity crisis in freshwater ecosystems, which exhibit higher rates of extinction and a greater proportion of threatened and endangered species than in terrestrial or marine environments, said Johnson.

The study appeared as the cover story in the September issue of Frontiers in Ecology and the Environment, a publication of the Ecological Society of America.

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